maintenance of capillary gc columns - young incoating efficiency: retention index: peak height...

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Young In Scientific Co., Ltd.

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Lee, Do-Woo

Maintenance of Capillary GC ColumnsMaintenance of Capillary GC Columns

or...."It's not what your column can do for you, but what you can do for your column"


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Objectives

• To know correct column installation procedure

• To know why column performance decreases

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Contents

1. Column Installation Procedure

2. To know correct column installation procedure

3. Column Storage

4. Summary


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Column Installation Procedure

1. Install the column

2. Leak and installation check

3. Column conditioning

4. Setting linear velocity or flow rate

5. Bleed profile

6. Test mix

"Getting off to a good start"

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Cutting The Column

Gently scribe through the polyimide coating.Do not attempt to cut the glass.

Recommended tools:Diamond or carbide tipped pencil; or sapphire cleaving tool, ceramic wafer Ocular

Do not use:Scissors, file, etc.

Install The Column


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Examples of Column Cuts

Good

Bad

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Column Installation

White out Septa

Measuring the right distance


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Column Installation

How tight is tight?

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Overtightened Ferrule


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2. Leak and Installation Check

Electronic leak detector

IPA/Water

Inject a non-retained peak

Leak Check

DO NOT USE SNOOP

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Leak and Installation Check

The peak should be sharp and symmetrical

Detector Compound

FID Methane or Butane

ECD MeCl2 (headspace or diluted)NPD CH3CN (headspace or diluted)TCD AirMS Air or Butane

Inject a non-retained compound vs DB-1


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Non-Retained Peak Shapes

Good Installation Improper Installation orInjector Leak

Check for: Injector or septum leakToo low of a split ratioLiner problem (broken, leaking, misplaced) Column position in injector and detector

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3. Column Conditioning

System must be leak free before conditioning column

Heat the column to the lower of:Isothermal maximum temperatureOR20° to 30°C above highest operation temperatureTemperature programming is not necessary

Stop conditioning when the stable baseline is obtained:1 to 2 hours in most cases


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Calculating Linear VelocityInject a non-retained compound and obtain the retention time:

µ is dependent on column temperature

µ=toL µ = Average linear velocity (cm/sec)

L = Column length (cm)to = Retention time (sec)

He 35-40 cm/secH2 45-60 cm/sec

4. Setting Linear Velocity or Flow Rate

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F is dependent on column temperatureMeasuring flow with a flow meter is often inaccurate

F = Flow rate (mL/min)r = Column radius (cm)L = Column length (cm)to= Retention time (sec)

=F r2Lto

Inject a non-retained compound and obtain the retention time:

4. Setting Linear Velocity or Flow Rate

Calculating Flow Rate


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Generating a Bleed Profile

*DB-1 30m x .32mm x .25µmTemperature program

40°C, hold 1 min20°/min to 320°Chold 10 min.

Temperature program the column without an injection*

Time (min.)0 5 10 15 20 25

6000

7000

8000

9000

1.0e4

1.1e4

1.2e4

1.3e4

5. Bleed Profile

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6. Test Mixes

Used to determine how "good" the column is

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Column Performance Summary

THEORETICAL PLATES/METER: MIN SPEC ACTUAL

COATING EFFICIENCY:

RETENTION INDEX:

PEAK HEIGHT RATIO:

MIN SPEC MAX SPEC ACTUAL

PENTADECANE

PENTADECANE

1-UNDECANOL

ACENAPHTHYLENE

4-CHLOROPHENOL/METHYL NONANOATE

4-PROPYLANILINE/METHYL NONANOATE

0.83

1.14

1371.04 1372.04 1371.43

1459.34 1460.34 1459.53

3900 4389

90.0 95.5

COMPOUNDIDENTIFICATION

RETENTION TIME(Tr )

PARTITION RATIO

(k)

PEAK WIDTH(W 1/2)

1,6-HEXANEDIOL

4-CHLOROPHENOL

METHYL NONANOATE

4-PROPYLANILINE

TRIDECANE

1-UNDECANOL

ACENAPHTHYLENE

PENTADECANE

2.51

2.95

3.21

3.81

4.20

5.52

8.00

9.58

0.9

1.3

1.5

1.9

2.2

3.3

5.2

6.4

0.019

0.022

0.022

0.026

0.027

0.036

0.053

0.062

PART NO:COLUMN I.D. NO.:LIQUID PHASE:FILM THICKNESS:COLUMN DIMENSIONS:

m X mmTEMPERATURE LIMITS:

C TO C

12250323303121

DB-50.25 µm

30 0.252

-60° 325° ( C PROGRAM)350°

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Chromatographic Performance

RETENTION TIME (MIN)

Max.Bleed10.0 pA325

9.0 pA

135

0 5

TEST TEMPERATURE:CARRIER GAS: (H2) 38.7cm/sec, 1.2ml/minINJECTION:ANALYST ERIK

135 C

SPLIT


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Test Mixture Components

Compounds Purpose

Hydrocarbons EfficiencyRetention

Alcohols ActivityFAME’s, PAH’s RetentionAcids Acidic CharacterBases Basic Character

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Own Test Mixture

• More specific

• Selective detectors

• Actual concentrations

• No conditions or instrument changes


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An Ounce of Prevention......

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Common Causes of Column Performance Degradation

1. Physical damage to the polyimide coating

2. Thermal damage

3. Oxidation (O2 damage)

4. Chemical damage by samples

5. Contamination


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1. Physical Damage to The Polyimide Coating

• Bending radius decreases with increasing tubing diameter

• Avoid scratches and abrasions

• Immediate breakage does not always occur upon physical damage

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2. Thermal Damage

Degradation of the stationary phase is increased at higher temperatures. Breakage along the polymer backbone.

Dimethylpolysiloxane

CH3 CH3CH3

CH3 CH3CH3

O

Si SiSi

OOO


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Thermal Damage

Disconnect column from detector

“Bake out” overnight at isothermal limit

Remove 10-15 cm from column end

What To Do If It Happens

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Thermal Damage

Rapid degradation of the stationary phase caused by excessively high temperatures

Isothermal limit = Indefinite time

Programmed limit = 5-10 minutes

Temporary "column failure" below lower temperature limit


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3. Oxidation (O2 Damage)

Oxygen in the carrier gas rapidly degrades the stationary phase.The damage is accelerated at higher temperatures. Damage along the polymer backbone is irreversible.

O2

CH3 CH3CH3

CH3 CH3CH3

O

Si SiSi

OOO

Dimethylpolysiloxane

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Oxygen Damage

• Rapid damage to the column

• Usually results in irreversible column damage



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How to Prevent Column Damage by Oxygen

• High quality carrier gas (4 nine's or greater)

• Leak free injector and carrier linesChange septaMaintain gas regulator fittings

• Appropriate impurity traps

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Configurations for Carrier Gas Purifiers

OVEN TEMP 100

IndicatingMoisture Trap

High CapacityOxygen Trap

Indicating Oxygen Trap

GC

Make sure the traps are in the upright position!


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4. Chemical Damage by Sample

Bonded and cross-linked columns have excellent chemical resistance except for inorganic acids and bases

Chemical damage will be evident by excessive bleed, lack of inertness or loss of resolution/retention lack of inertness or loss of resolution/retention

HCl NH3 KOH NaOH

H2SO4 H3PO4 HF etc.

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Chemical Damage

• Remove 1/2 - 1 meter from the front of the columns

• Severe cases may require removal of up to 5 meters



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5. Contamination

Fouling of GC and column by contaminants

Mimics nearly every chromatographic problems

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Symptoms of Contamination

• Poor peak shape

• Loss of separation (resolution)

• Changes in retention

• Reduced peak size

• Baseline disturbances (semi-volatiles only)


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Typical Samples Containing Large Amount of Residues

Biological (Blood, Urine, Tissue, Plants)

Soils Foods

Waste Water Sludge

All samples contain residues!!

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Other Sources of Contamination

Septum and ferrule particles

Gas and trap impurities

Unknown sources (vials, syringes,etc.)


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Non-Volatile Residues

Any portion of the sample that does not elute from the column or remains in the injector.

Semi-Volatile Residues

Any portion of the sample that elutes from the column after the current chromatographic run.

Other Sources of Contamination

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Methods to Minimize Non-Volatile Residue Problems

Sample cleanup

Packed injection port liners

Guard columns


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Guard Column

The guard column is 0.5 - 10 meters of deactivated fused silica tubing with the same diameter as the analytical column. It is connected with a zero dead volume union.

INJECTORDETECTOR

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Non-Volatile Contamination

Do not “bake out” the column

Front End Maintenanceclean or change the injector linerclean the injectorcut off 1/2 -1 meter of the front of the column

Turn the column around

Solvent rinse the column

Cut the column in half



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Rinse Kit

1/16" flexible teflon line to regulated pressure source

Beaker for solvent collection

Capillary column Special connectorand ferrule

Flexible teflontubing

Special adapter

CapVial

Capillary column

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Semi-Volatile Contamination

“bake out” the columnLimit to 1-2 hoursMay polymerize some contaminationReduces column life

Solvent rinse the column



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Column Storage

• Place septa over the ends

• Return to column box

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Always Remember to:Always Remember to:

Start with a good installation

Maintain an oxygen free system

Avoid physical, thermal, and chemical damage

Take steps to prevent contamination

Summary


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Thank you very much for your attention !

maintenance of capillary gc columns - young incoating efficiency: retention index: peak height...

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